(a) Field of the Invention
The present invention relates to a stannic acid anhydride suitable for forming transparent conductive tin oxide, and to conductive products covered with tin oxide.
(b) Description of the Prior Art
In recent years, accompanied with the remarkable development in the field of electro-optical elements, attention is paid to transparent conductive films of the type of SnO.sub.2 or In.sub.2 O.sub.3. They are actively developed, for example, as transparent electrodes of various optical devices such as those of electro-luminescence, liquid crystals, image accumulation devices, etc.; as heating elements or resistors utilizing their heat resistance and anti-abrasion properties; as solar cells utilizing their high conductivity; or as selective permeable films for use in solar heat electricity generation utilizing their high reflexibility in infrared rays.
Among the methods of forming these transparent conductive films are known:
(1) chemical vapor deposition method, PA0 (2) vacuum evaporation method, PA0 (3) sputtering method, and PA0 (4) coating method.
Also, there is a strong demand for conductive powder to give conductivity to paints, plastics, fibers, etc., and for example, in Japanese Patent Kokai (Laid-open) No. 77623/1986, a method is proposed in which titanium oxide-tin oxide type composite conductive powder is produced by mixing prescribed quantities of stannous oxalate and antimony chloride with titanium oxide and baking the mixture.
All of the above-mentioned methods (1)-(3) use complicated apparatus and are inferior in operability. In addition, they usually necessitate an etching step after film formation, to form a pattern.
In the method (4) also, when using an inorganic salt such as SnCl.sub.4 for example, since hydrogen chloride or other chloride gases are generated upon heat decomposition, severe corrosion of the apparatus takes place. Also, the chlorine remaining in the film may impair conductivity. There are also methods using organic acid salts such as octyl acid tin salt or an organic complex. But in these methods, there are problems such that the uniformity of the film is impaired upon heat decomposition or gelation of the coating liquid takes place. Moreover, they have defects such that the formed film is uneven and cloudy, and is liable to become damaged.
By the method of the above-mentioned Japanese Patent Kokai, it is impossible to cover the surface of titanium oxide with tin oxide, so that not only is the conductivity insufficient but also the performance shows great fluctuation.
Taking the above-mentioned problems of the prior art into account, we carried on further studies, and as a result, we attained the present invention.
The object of the present invention is to provide a novel tin compound which has no restriction or problem on the apparatus, has high applicability, and can finally form tin oxide having excellent transparency and conductivity, in an industrially advantageous manner, and to provide products having a uniform tin oxide film formed on a substrate of any form such as powder form, film form, fiber form, etc. and therefore provides excellent conductivity.